Multiprocessor computer systems comprise a number of processing element nodes connected together by an interconnect network. Each processing element node includes at least one processing element. The interconnect network transmits packets of information or messages between processing element nodes. Multiprocessor computer systems having up to hundreds or thousands of processing element nodes are typically referred to as massively parallel processing (MPP) systems. In a typical multiprocessor MPP system, every processing element can directly address all of memory, including the memory of another (remote) processing element, without involving the processor at that processing element. Instead of treating processing element-to-remote-memory communications as an I/O operation, reads or writes to another processing element's memory are accomplished in the same manner as reads or writes to the local memory. In such multiprocessor MPP systems, the infrastructure that supports communications among the various processors greatly affects the performance of the MPP system because of the level of communications required among processors.
Several different topologies have been proposed to interconnect the various processors in such MPP systems, such as rings, stars, meshes, hypercubes, and torus topologies. For example, in a conventional hypercube network, a plurality of microprocessors are arranged in an n-dimensional cube where the number of nodes k in the network is equal to 2n. In this network, each node is connected to each other node via a plurality of communications paths. The network diameter, the longest communications path from any one node on the network to any other node, is n-links.
Regardless of the topology chosen, one disadvantage of current multiprocessor systems, and in particular MPP systems, is that in order to expand the system, a significant amount of reconfiguration is required. The reconfiguration often involves removing and replacing cables which is very time consuming. Also, as systems increase the number of processors, the number of physical connections required to support the system increases significantly which increases the complexity of the system.
Therefore, it is desired that systems could be easily scaled to increase the number of processors with minimal disruption to the original system configuration.